This comic shows two simple line graphs on the same chart. One shows society's expectations, the other what Randall actually felt. The visual joke is that the societal expectation graph is treated like an actual down-moving escalator, with people on it.

An escalator is a continuously moving mechanized stairway that travels in a particular direction, either up or down. Traditionally, people stop walking when riding the escalator, and simply stand (perhaps holding the hand-rail) until they reach the destination and then step off. However, if you are in a hurry or impatient, it is possible to also climb the stairs manually, increasing your effective speed of ascent or descent.

Young children are typically fascinated by escalators, and will often want to run up and down them just for fun. A variation is to travel the escalators in the opposite to the intended direction. Running up the down escalator is type of physical challenge, especially for younger children, as they are fighting gravity and the downward motion of the escalator to reach the top. If they pause or cannot keep up sufficient speed, the escalator will impersonally return them to their starting position.

The curved graph on the chart shows how the urge to run up the down escalator is expected to peak at about age 7 and then decline steeply as you approach adulthood, although never quite reaching zero. For Randall (it seems to be Randall who is speaking), the urge has not diminished in any way, and even seems to be showing an upward trend as the graph approaches 24 years of age.

He does not appear to have acted upon this urge very often; in fact he claims only once.

The title text refers to the Slinky toy, a coiled spring that is designed to go down stairs by itself in an amusing manner. Since the Slinky is moving with the flow, its effective speed is doubled. A normal Slinky is very small and would not be able to halt an average human being through its inertia, but it could tangle up in their feet or otherwise trip them up, and would at least be a surprising encounter.

[Graph with y axis titled "Urge to try running up the down escalator", with "weak" by the bottom and "strong" by the top. x axis has every two years labeled and every year signified by a smaller mark, which stops at 24. A red line with "What I was supposed to feel" with points at every line rises, peaks at 7 years old, then falls "tangent graph" shaped until the end. Along this line are shown various stick-figures at 12, 14, 20 and 24. A second red line runs "What I've actually felt" which stays consistently high.]

Discussion

I just wanted to point out that I think it's funny how in-depth some of these wiki's are and how others aren't. In this one we have good hearted contributors explaining what an escalator is, while in the last article I read the author uses NSFW as if it's common parlance. My rhetorical question is this: who, reading this article, immediately recognizes the acronym NSFW yet has no previous knowledge of escalators? Although not an Explain XKCD reader, my kindergartener has less knowledge of work ethics (let alone Internet slang regarding work ethics) yet has a basic understanding of escalators in popular culture, including the phenomenon of "running up the down". That is all ;) 71.154.215.156 17:51, 10 May 2013 (UTC)

Welcome to public wiki's ;-) You get what people are willing to write. Both articles could do with some wikilinks. Mark Hurd (talk) 18:37, 10 May 2013 (UTC)

Haha! I suppose someone who spends all his time indoors on the internet would understand NSFW but not an escalator. Maybe that's who I was writing for. And maybe that says too much about my life. ;) --Druid816 (talk) 21:54, 16 May 2013 (UTC)

I've confirmed "tangent graph" is from the official transcript, but it doesn't look like a tangent graph, except perhaps on its side. It looks more like a bell curve to me. Mark Hurd (talk) 10:18, 26 May 2013 (UTC)

I have to assume by "tangent graph" he doesn't literally mean a graph of the trigonometric tangent function, but a graph that shows an asymptotic approach to a particular value (in this case, probably zero). 108.162.219.223 19:14, 17 January 2014 (UTC)

I changed the explanation to make it less about what an escalator is, and more about the intent behind the joke. 108.162.219.223 19:14, 17 January 2014 (UTC)

It depends on what kind of escalators it is. If you are running up the 70-meter-long down escalator which has a Chin-Up Bar at the end of it, you should feel like what you was supposed to feel.--Handbug (talk) 04:19, 11 September 2014 (UTC)

It also depends on whether you have need of doing this, for example if you are rushing to the metro station finding an overcrowded upward escalator and a sparsely crowded downward escalator every day, then you will have much strong urge to put in that chart.--Handbug (talk) 04:23, 11 September 2014 (UTC)

I've actually run up a down escalator. It was: 1) exciting, and 2) actually pretty hard to do. Leafy Greens (talk) 02:40, 16 November 2014 (UTC)

One could also interpret the graph as the y axis as the altitude on an escalator and the x axis as time. If someone started running up the down elevator as soon as they got on, their altitude would remain at the top, whereas if someone rode the elevator down, their altitude would go down as shown in the graph. Phlaxyr (talk) 20:47, 21 July 2016 (UTC)

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